Neutron Scattering Study of URu$_{1.9}$Re$_{0.1}$Si$_{2}$: Driving Hidden Order Towards Quantum Criticality

We report inelastic neutron scattering measurements in the hidden order state of URu$_{1.9}$Re$_{0.1}$Si$_{2}$. We have fit the data to a resolution convolved simple harmonic oscillator model, plus a continuum extending to 10meV. We observe that towards the Quantum Critical Point (QCP) induced by Re-doping, the gapped incommensurate fluctuations are fairly robust, being nearly identical to the parent material. The gap at the commensurate point (1 0 0) is driven down as the doped system approaches the QCP. The response of this commensurate spin fluctuation associated with the hidden order acquires substantial damping. The particle-hole spectrum of nested fermions [1] can be fitted to the energy and damping of the excitations, but there is no evidence for the static charge density wave that the model implies [2], in agreement with STM [3]. We conclude that Re-doping weakens, but does not destroy, the hidden order on approaching the QCP transition to ferromagnetism. \newline [1] Balatsky et al. Phys. Rev. B 79 (2009) 214413 \newline [2] Su et al. arXiv/cond-mat:1010.0767 (2010) \newline [3] Schmidt et al. Nature 465 (2010) 570 \newline Research at UCSD supported by U.S. DOE Grant \#DE-FG02-04ER46105.